1. Technical Field
The invention relates to a wide-angle imaging lens installed into a camera mounted on a vehicle, a mobile phone camera, a surveillance camera, and the like using an imaging device such as CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), and an imaging device and a camera module for converting an optical image captured by the wide-angle imaging lens into an imaging signal.
2. Description of the Related Art
In order to shoot a wide range, a superwide-angle type shooting lens having a wide angle of view is used in a surveillance camera and a camera mounted on a vehicle. In order to further accomplish a superwide angle, the number of lenses tends to increase. However, Patent Documents 1 to 4 (see below) disclose a wide angle lens in which a relatively small number of lenses, i.e., six lenses in total are employed to attempt to attain a size reduction and a weight reduction while aspheric lenses are used effectively to keep good optical performance. The wide-angle lenses disclosed in Patent Documents 1 to 4 are constructed such that first to third lenses are arranged on the front side to put an aperture stop therebetween and that fourth to sixth lenses are arranged on the image side. In these wide-angle lenses, a cemented lens is used to correct a chromatic aberration. In particular, in the wide-angle lenses disclosed in Patent Documents 1 to 3, the fourth lens and the fifth lens located close to the aperture stop are formed of the cemented lens. In this case, the fourth lens is a negative lens and the fifth lens is a positive lens. In the wide angle lens disclosed in Patent Document 4, the fifth lens and the sixth lens located away from the aperture stop are formed of the cemented lens. In this case, the fifth lens is a negative meniscus lens and the sixth lens is a biconvex lens. Also, in the wide angle lens disclosed in Patent Document 4, a surface located closest to the image side (the surface of the sixth lens on the image side) is formed into the aspheric surface.
[Patent Document 1] JP 2003-232998 A
[Patent Document 2] JP 2005-221920 A
                (corresponding to US 2005/0174463 A)[Patent Document 3] JP 2006-119368 A        (corresponding to US 2006/0087747 A)[Patent Document 4] Japanese Patent No. 2599312        
However, in the wide-angle imaging lenses disclosed in the above Patent Documents, the maximum angle of view is 150° or so. Hence, it is demanded to realize a lens having a wider angle of view, e.g., a lens in which a further increase of a super-wide angle is achieved to get the maximum angle of view of 180° or more. In this case, it is desirable that a small-size and lightweight configuration is still kept without increase in the number of lenses.